The former school principal of Pei Chun Public School has been sentenced to nine weeks' jail for having commercial sex with a minor.

Lee Lip Hong, 39, is the first man to be sentenced to jail in the underaged callgirl scandal after being the first of 48 men to plead guilty on Friday morning.

Dressed in a suit, Lee admitted in court to one of two charges of having paid $500 for sex with the girl, who was 17 at the time, at Hotel 81 Bencoolen in September 2010. The other charge has been considered for sentencing.